Surely what matters in this discussion is where the "continental
divide" is between Europe and Asia? European stations are presumably
Z16, Asian Z17.

Art RX9TX has pointed out that the UA9S and UA9T suffixes are
assigned randomly within Orenburg oblast, so that distinction doesn't
help.

The Ural River flows through Orenburg city and oblast, and is shown
in my National Geographic atlas as the boundary between Europe and
Asia. This fits Art's suggestion that stations northwest of the river
are in Europe Z16, and those southeast of it (like himself) are in
Asia Z17 (correct Art?).

No matter. I learned sometime back that a station's Zone is what CQ
says it is! The 9M0s on Layang-Layang atoll in the Spratly chain are
about 100mi outside the eastern boundary of Z26 on most maps - but
they count for Z26 (fortunately!).